Some member in this forum actually welcome the 60D with plastic body for the lighter weight. One member actualy suggest team up a light weight DSLR body with a light weight plastic lens (50mm f1.8 II). It is a mistake. I am not against plastic body but I am against lightweight. It is just simple physics. 1. When we push the shutter release button, our hand do have the tendency to move. The heavier the camera, the less movement it will be. 2. After the shutter button is pushed. The mirror will flip up and the camera body will come down (conservation of momentum). The heavier the camera , the slower the camera movement. We know that any movement during the exposure will cause unsharpness of the picture. So a heavier camera will have less and slower movement and hence a sharper picture. In the old film dates, people actually attach lead plate on the light weight SLR to minimize camera movement.
So let me translate this for everyone:
"I've never used a light weight camera plus light weight lens and I've never used a heavy camera plus heavy lens so let me make a guess about what happens based on an incorrect model I've built and applied some physics to."
Why don't you buy yourself a camera or two and a lens or two and go out and try the various combinations out for us and report back to us on the real world impact of the choices vs the predictions from physics?